U.S. patent application number 09/805328 was filed with the patent office on 2001-12-20 for window portion with an adjusted rate of wear.
Invention is credited to Budinger, William D., Kubo, Naoto.
Application Number | 20010053658 09/805328 |
Document ID | / |
Family ID | 22697114 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053658 |
Kind Code |
A1 |
Budinger, William D. ; et
al. |
December 20, 2001 |
Window portion with an adjusted rate of wear
Abstract
A polishing pad includes a polishing layer, and the transparent
window portion of the polishing layer having dispersed particles to
increase the rate at which the window portion wears away during a
polishing operation, and to avoid forming a lump in the polishing
layer.
Inventors: |
Budinger, William D.; (Key
West, FL) ; Kubo, Naoto; (Nara Pref, JP) |
Correspondence
Address: |
Rodel Holdings, Inc.
Suite 1300
1105 North Market Street
Wilmington
DE
19899
US
|
Family ID: |
22697114 |
Appl. No.: |
09/805328 |
Filed: |
March 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60189386 |
Mar 15, 2000 |
|
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Current U.S.
Class: |
451/41 ; 451/527;
451/59 |
Current CPC
Class: |
B24B 49/12 20130101;
B24B 37/205 20130101 |
Class at
Publication: |
451/41 ; 451/59;
451/527 |
International
Class: |
B24B 001/00; B24D
011/00 |
Claims
What is claimed is:
1. A polishing pad for polishing semiconductor wafers, comprising:
a polishing layer having a transparent window portion; the
transparent window portion being constructed of a wear resisting
material with an inherent resistance to wear when subjected to
abrasion during a polishing operation; the rate at which the window
portion wears away during the polishing operation being increased
to avoid forming a lump in the polishing layer, by having dispersed
particles of at least one, or more than one, substance dispersed
throughout the window portion; and the particles providing
discontinuities in the wear resisting material, which are
susceptible to wear when subjected to abrasion during the polishing
operation.
2. The polishing pad as recited in claim 1 wherein, the dispersed
particles are pieces of solid matter having a lower resistance to
wear than that of the wear resisting material.
3. The polishing pad as recited in claim 1 wherein, the dispersed
particles are pieces of solid matter that are susceptible to being
snagged and worn away when subjected to abrasion during the
polishing operation.
4. The polishing pad as recited in claim 1 wherein, the dispersed
particles are cells of entrapped fluid within the wear resisting
material; and the cells are susceptible to being snagged and worn
away when subjected to abrasion during the polishing operation.
5. The polishing pad as recited in claim 4 wherein, the entrapped
fluid is air.
6. The polishing pad as recited in claim 4 wherein, the entrapped
fluid is deionized water.
7. The polishing pad as recited in claim 4 wherein, the cells are
in the form of bubbles containing the entrapped fluid.
8. The polishing pad as recited in claim 1 wherein, the wear rate
of the window portion is adjusted to be greater than that of the
remainder of the polishing layer, which reduces a force exerted
normal to the window portion as the window portion wears away
during the polishing operation.
9. The polishing pad as recited in claim 1 wherein, the wear rate
of the window portion is adjusted to be substantially equal to that
of the remainder of the polishing layer, which evenly distributes a
force exerted normal to the polishing layer during the polishing
operation.
10. A method of polishing a semiconductor wafer with a polishing
pad having a polishing layer with a transparent window portion,
comprising the steps of: providing dispersed particles of at least
one, or more than one, substance dispersed throughout the window
portion to increase the rate at which the window portion wears away
during a polishing operation and to avoid forming a lump in the
polishing layer, and polishing the semiconductor wafer with the
polishing layer having the transparent window portion, and the
particles providing discontinuities in the wear resisting material,
which are susceptible to wear when subjected to abrasion during the
polishing operation, without the window portion forming a lump in
the polishing layer.
11. The method as recited in claim 10 wherein, the step of
providing the dispersed particles, further includes the step of:
providing the dispersed particles as pieces of solid matter having
a lower resistance to wear than that of the wear resisting
material.
12. The method as recited in claim 10 wherein, the step of
providing the dispersed particles, further includes the step of:
providing the dispersed particles as pieces of solid matter that
are susceptible to being snagged and worn away when subjected to
abrasion during the polishing operation.
13. The method as recited in claim 10 wherein, the step of
providing the dispersed particles, further includes the step of:
providing the dispersed particles as cells of entrapped fluid; and
the nanometer sized cells are susceptible to being snagged and worn
away when subjected to abrasion during the polishing operation.
14. The method as recited in claim 10 wherein, the step of
providing the dispersed particles, further includes the step of:
providing the dispersed particles as cells of entrapped air.
15. The method as recited in claim 10 wherein, the step of
providing the dispersed particles, further includes the step of:
providing the dispersed particles as cells of deionized water.
16. A method of making a window portion of a polishing pad,
comprising the steps of: providing a transparent window portion of
a polishing layer with dispersed particles of at least one, or more
than one, substance to increase the rate at which the window
portion wears away during a polishing operation and to avoid
forming a lump in the polishing layer.
17. A polishing pad useful for polishing integrated circuit wafers,
comprising: a polishing surface and a transparent window portion
disposed in an opening in the polishing surface, wherein the window
portion has a wear rate equal to or greater than that of the
polishing surface.
18. A pad according to claim 17, wherein the window portion is
comprised of a polyurethane having a wear rate of from 5 to 25%
greater than the wear rate of the polishing surface.
19. A pad according to claim 17, wherein the window portion is
comprised of polymethylmethacrylate or polycarbonate.
20. A pad according to claim 17, wherein the window portion
comprises a discontinuity selected from solid particles, fluids and
gases.
21. A pad according to claim 17, wherein the window portion
comprises a polyurethane and a discontinuity selected from solid
particles, fluids and gases.
22. A pad according to claim 21, wherein the discontinuity is a
plastic particle.
23. A pad according to claim 22, wherein the diameter of the
particle is from 10-20 .mu.m.
24. A pad according to claim 21, wherein the window portion
comprises from 1 to 10% by weight of the particles.
25. A pad according to claim 21, wherein the window portion
comprises polyurethane and the plastic particle is
polyurethane.
26. A pad according to claim 21, wherein the discontinuity is a
fluid.
27. A pad according to claim 26, wherein the fluid comprises from 1
to 10% by weight of the window portion.
28. A pad according to claim 26, wherein the fluid is a hydrocarbon
oil.
27. A pad according to claim 26, wherein the fluid is mineral
oil.
27. A pad according to claim 21, wherein the discontinuity is a
gas.
28. A pad according to claim 27, wherein the gas is carbon dioxide,
nitrogen, or air and the gas comprises 85 to 99% of the volume of
the window portion.
29. A pad according to claim 17, wherein the transparent window
portion comprises: a silica aerogel.
30. A pad according to claim 29, wherein the silica aerogel is
prepared from tetramethyl orthosilicate or tetraethyl
orthosilicate.
31. A pad according to claim 21, wherein the discontinuity is an
immiscible polymer system.
32. A pad according to claim 31, wherein the immiscible polymer
system is polyurea/polyurethane or nitrocellulose/acrylic.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional
application serial No. 60/189,386, filed Mar. 15, 2000.
FIELD OF THE INVENTION
[0002] The invention relates to a polishing pad having a
transparent window portion in a polishing layer.
DISCUSSION OF RELATED ART
[0003] A polishing operation is performed on a semiconductor wafer
to remove excess material, and to provide the wafer with a smooth,
planar polished surface. To attain the smooth, planar polished
surface, the polishing layer of the polishing pad provides a
uniform polishing action. During the polishing operation, polishing
pressure is exerted on the window portion and on the remainder of
the polishing layer.
[0004] U.S. Pat. No. 5,893,796 discloses a known polishing pad
having a transparent window portion installed in a polishing layer
of the polishing pad. It has been found that the window portion was
fabricated with materials that have an inherent resistance to wear.
Other materials in a remainder of the polishing layer have a lower
resistance to wear. Thus, as a polishing layer slowly wears away as
it is being used to polish a semiconductor wafer, the transparent
window portion wears away more slowly, at a lower rate of wear. As
a result, the transparent window portion becomes a lump on the
polishing layer, the lump having a height greater than the height
of the remainder of the polishing layer.
[0005] The window portion, being a lump on the polishing layer, is
pressed inward by the polishing pressure to become flush with the
polishing surface. However, the inwardly pressed window portion
polishes with a different polishing action than that of the
remainder of the polishing layer. For example, the window portion,
as a lump, concentrates polishing force against the semiconductor
wafer, which produces a nonuniform polishing action. Consequently,
the nonuniform polishing action produces defects in the smooth,
planar polished surface on the semiconductor wafer.
[0006] A need exists for a polishing pad having a polishing layer
with a transparent window portion, which provides a uniform
polishing action as the polishing layer undergoes wear during a
polishing operation.
[0007] Further a need exists for a transparent window portion that
avoids becoming a lump on a worn polishing layer of a polishing
pad.
SUMMARY OF THE INVENTION
[0008] According to the invention, a transparent window portion of
a polishing layer is provided with dispersed particles of at least
one, or more than one, substance dispersed throughout the window
portion to increase the rate at which the window portion wears away
during a polishing operation and to avoid forming a lump in the
polishing layer.
[0009] Embodiments of the invention will now be described by way of
example with reference to the following detailed description.
DETAILED DESCRIPTION
[0010] Embodiments of the invention will now be described by way of
example with reference to the following detailed description.
[0011] A semiconductor wafer having integrated circuits fabricated
thereon must be polished to provide a very smooth and flat wafer
surface which in some cases may vary from a given plane by as
little as a fraction of a micron. Such polishing is usually
accomplished in a chemical-mechanical polishing (CMP) operation
that utilizes a chemically active slurry that is buffed against the
wafer surface by a polishing pad. Methods have been developed for
determining when the wafer has been polished to a desired endpoint.
According to U.S. Pat. No. 5,413,941, one such method includes
light generated by a laser to measure a wafer dimension.
[0012] According to a known polishing pad, the surface of the
transparent window portion is flush with the polishing surface of
the polishing pad. The window portion and the polishing surface are
in contact with the workpiece, i.e. semiconductor wafer, being
polished.
[0013] When the window portion has a wear rate that is lower (i.e.,
it wears slower) than that of the polishing surface surrounding it,
the polishing layer wears away at a rate that is faster than the
rate at which the window portion wears away. The height of the
window portion becomes greater than the height of the polishing
layer. The performance of the polishing pad is jeopardized.
[0014] A polishing operation is performed on a semiconductor wafer
to remove excess material, and to provide the wafer with a smooth,
planar polished surface. To attain the smooth, planar polished
surface, the polishing layer of the polishing pad provides a
uniform polishing action. During the polishing operation, polishing
pressure is exerted on the window portion and on the remainder of
the polishing layer. The window portion, being a lump on the
polishing layer, is pressed inward by the polishing pressure to
become flush with the polishing surface. However, the inwardly
pressed window portion polishes with a different polishing action
than that of the remainder of the polishing layer. For example, the
window portion, as a lump, concentrates polishing force against the
semiconductor wafer, which produces a non-uniform polishing
action.
[0015] Examples of such pads include urethane impregnated polyester
felts, microporous urethane pads of the type sold as Politex.RTM.
by Rodel, Inc. of Newark, Del., and filled and/or blown composite
urethanes such as IC-series and MH-series polishing pads also
manufactured by Rodel, Inc. of Newark, Del. Window portions used in
these types of urethane pads typically comprise urethane with the
standard additives in the Politex.RTM. and IC- and MH-series.
[0016] A known polymeric pad has a matrix that comprises materials
selected from polyurethanes, acrylics, polycarbonates, nylons,
polyesters, polyvinyl chlorides, polyvinylidene fluorides,
polyether sulfones, polystyrenes, and polyethylenes, polyurethanes,
acrylics, polycarbonates, nylons, and polyesters with higher wear
rates than the currently used polyurethanes.
[0017] A known polymeric matrix that can be used according to the
invention comprises materials selected from polyurethanes,
acrylics, polycarbonates, nylons, polyesters, polyvinyl chlorides,
polyvinylidene fluorides, polyether sulfones, polystyrenes,
polyethylenes, FEP, Teflon AF.RTM., and the like. Other materials
are polyurethanes, acrylics, polycarbonates, nylons, polyesters and
polyurethanes. Further examples include polymethylmethacrylate
sheets (e.g., Plexiglas.RTM. sold by Rohm and Haas, Philadelphia,
Pa.) and polycarbonate plastic sheets (e.g., Lexan.RTM. sold by
General Electric). Casting or extruding the polymer and then curing
the polymer to the desired size and thickness can make the window
portions.
[0018] The polishing pad comprises a polymeric matrix formed from
urethanes, melamines, polyesters, polysulfones, polyvinyl acetates,
fluorinated hydrocarbons, and the like, and mixtures, copolymers
and grafts thereof. The polymeric matrix comprises a urethane
polymer. The urethane polymer is advantageously formed from a
polyether-based liquid urethane, such as the Adiprene.TM. line of
products that are commercially available from Uniroyal Chemical
Co., Inc. of Middlebury, Conn. For example, a liquid urethane
contains about 9 to about 9.3% by weight free isocyanate. Other
isocyanate bearing products and prepolymers may also be used. The
liquid urethane is advantageously one which reacts with a
polyfunctional amine, diamine, triamine or polyfunctional hydroxyl
compound or mixed functionality compounds such as hydroxyl/amines
dwelling in urethane/urea crosslinked networks to permit the
formation of urea links and a cured/crosslinked polymer network.
The liquid urethane is reacted with
4,4'-methylene-bis(2-chloroaniline) ("MOCA"), which is commercially
available as the product CURENE.RTM. 442, from Anderson Development
Co. of Adrian, Mich.
[0019] Forming a window portion comprising a phase separated or
biphasic system is accomplished by blending two immiscible polymers
until their domain size will not scatter light and then
polymerizing them in the shape of a window portion. The immiscible
polymer is expected to provide a window portion with particulates
of immiscible polymer providing an increased WR. Pairs of
immiscible polymers can include, but are not limited to,
polyurea/polyurethane, nitrocellulose/acrylic and the like.
[0020] If the wear rate (WR) of the transparent window portion is
equal to or greater than the WR of the polishing surface, then the
window portion will be expected to remain flush with the polishing
surface during a polishing operation. Wear rate is a measure of how
quickly the surface of the window portion surface or polishing
surface is removed, or worn away, during chemical-mechanical
polishing. Abrasion resistance, or resistance to abrasion, is a
measure of how the surface of the window portion or of the
polishing surface avoids being removed or worn away by abrasion
during chemical-mechanical polishing. The invention provides a
transparent window portion that has a higher wear rate and lower
abrasion resistance than window portions fabricated with materials
having inherently high resistance to wear, as in previous polishing
pads. Advantageously, the WR.sub.window portion is equal to or at
least 5, 10, 15, 20, 25, 50, 100, or 200% greater than WR.sub.pol
surface. More advantageously, the WR.sub.window portion is 5, 10,
15, 20, to 25% greater than WR.sub.pol surface.
[0021] The invention provides a transparent window portion
comprised of a polymeric matrix further comprising a discontinuity
that increases the wear rate (or decreases the abrasion resistance)
of the window portion compared with the polymeric matrix without
the discontinuity.
[0022] Discontinuity, as used herein, is intended to mean that the
polymeric matrix has been disrupted by the presence of a foreign
material. A desired discontinuity is one that increases the WR of
the polymeric matrix. The amount of the disruption or discontinuity
depends on the desired WR of the polymeric matrix. Discontinuities
can be obtained by the forming the polymeric matrix in the presence
of solid particles, fluids, gases, or an immiscible polymer system.
The polymeric matrixes are prepared so that the discontinuities do
not mechanically reinforce the matrix or are so large as to cause
scattering of an incident optical beam that prohibits optical
end-point detection. Additives can include solid particles (e.g.,
silica, titania, alumina, ceria, or plastic particles).
Advantageously the additives are plastic particles. Nanometer sized
particles, are particles of one nanometer and less in size, that
are of sufficiently low surface area to avoid scattering of
incident light. Dispersal of the particles in the window portion,
rather than agglomeration of the particles, further avoids
scattering of incident light.
[0023] The particles (e.g., plastic particles) can range in
diameter from 1 nm to 200 .mu.m, advantageously from 1 to 50 .mu.m,
more advantageously from 10-20 .mu.m. The actual shape of the
plastic particles is not limited. It can include chips, squares,
discs, pucks, donuts, spheres, cubes, irregular shapes, etc.
Advantageously, from 1, 2, 3, 4, 5, 6, 7, 8, 9 to 10% of the weight
of the window portion is from the solid particles.
[0024] The plastic comprising the particles is chosen depending on
the polymeric matrix of the window portion. The plastic is chosen
such that its presence has little or no effect on the index of
refraction of the window portion. Advantageously the plastic has
about the same index of refraction as the polymeric matrix of the
window portion. Advantageously the plastic is the same as the
polymeric matrix of the window portion. Thus, the plastic can be
selected from polyurethanes, acrylics, polycarbonates, nylons,
polyesters, polyvinyl chlorides, polyvinylidene fluorides,
polyether sulfones, polystyrenes, and polyethylenes.
Advantageously, the plastic is selected from polyurethanes,
acrylics, polycarbonates, nylons, and polyesters. More
advantageously, the plastic is polyurethane.
[0025] Fluids in the form of a polymeric emulsion are expected to
create a discontinuity. By forming the window portion in the
presence of a fluid, a polymeric matrix can be obtained that
encapsulates the fluid in individual, spaced cells, including
bubbles. This is expected to increase the WR of the window portion.
Advantageously, from 1, 2, 3, 4, 5, 6, 7, 8, 9 to 10% of the weight
of the window portion is from the fluid. For example, such fluids
or liquids include hydrocarbon oils such as mineral oil.
[0026] Another discontinuity can be the presence of a gas in the
polymeric matrix. By forming the window portion in the presence of
a gas type fluid, a polymeric matrix can be obtained that
encapsulates the fluid in individual, spaced cells, including
bubbles. Advantageously, from 85, 86, 87, 88, 89, 90, 91, 92, 93,
94, 95, 96, 97, 98 to 99% of the volume of the window portion is a
gas (e.g., air, carbon dioxide, or nitrogen). For example, an
aerogel is a silica aerogel. The silica aerogels are prepared from
silicon alkoxides, advantageously tetramethyl orthosilicate or
tetraethyl orthosilicate.
[0027] The transparent window portion of the present invention
should be transparent to light having a wavelength within the range
of 190 to 3500 nanometers, depending on the application and optical
device being used to monitor the polishing process. The transparent
window portion should also be transparent to allow for optical
end-point detection of the device being polished.
[0028] Embodiments of the invention having been disclosed, other
embodiments and modifications of the invention are intended to be
covered by the spirit and scope of the appended claims.
* * * * *